This invention relates to a process for producing alkynols by a low pressure ethynylation reaction from an aldehyde and an acetylene in the presence of a catalyst comprising a copper acetylide complex supported on a transitional alumina carrier.
Alkynols are prepared in accordance with the well known processes such as those described in U.S. Pat. Nos. 2,232,867; 2,300,969; 2,487,006-9; 2,712,560; 2,768,215; 3,108,104; 3,294,849; and 3,560,576, viz., by reacting aldehydes with an acetylenic hydrocarbon of the general formula R--C.tbd.C--H, wherein R represents hydrogen or the radical of a hydrocarbon, such as methyl, vinyl, or phenyl. The acetylene or acetylenic hydrocarbon is introduced into the reaction zone as a gas, while the aldehyde can be a liquid under reaction conditions, or can be present in a liquid solvent or diluent. Typically, the reaction involves the reaction of acetylene and formaldehyde to yield butynediol and propargyl alcohol. It is known that the reaction proceeds at moderately elevated temperatures of from 50.degree. to 150.degree. C. at superatmospheric pressures, generally from 2 to 30 atmospheres. It has been stated to be desirable to conduct the reaction at a pressure less than 10 atmospheres and with careful temperature control to reduce the danger of explosion. Even at these pressures, the acetylene gas has been diluted with inert gases or vapors e.g., nitrogen, hydrogen or carbon dioxide in order to reduce the danger of explosion. However, even under these conditions, the danger of explosion still exists with the prior art processes.
The above-mentioned ethynylation reactions generally employ some form of cuprous acetylide complex catalyst, either supported or unsupported, which catalyst may be generated or made active by a variety of methods and from a variety of copper compounds. Often they are used together with a bismuth compound to minimize undesired cuprene formation, minimizing undesired acetylene polymerization. Supported catalysts used in the high pressure reaction systems are produced by impregnating the support with a solution of bismuth and copper salts such as the nitrates, drying and calcining to produce the metal oxides. The copper oxide thereafter is converted to an acetylide complex in situ by suitable treatment with acetylene and formaldehyde.
To achieve low ethynylation operating costs, it has been preferred to use the supported catalyst in pellet form in a fixed bed, plug flow process. Dilute aqueous formaldehyde and injection of acetylene at relatively high pressure are employed to convert excess formaldehyde and minimize distillation requirements to produce a product of requisite purity. However, this approach has necessitated high reactor costs to permit use, not only at normal acetylene operating pressures of up to 26 atmospheres, but also at the high pressures of up to 20 times greater than normal which occur coincidentally with the occasional acetylene decomposition which occurs at high pressures.
It has been proposed to employ such supported catalysts as slurries in continuous agitated reactions. Hitherto in such systems, however, not only has it been found necessary to remove and purify the catalyst at frequent intervals to avoid fouling, but even with continuous complete catalyst purification and recycle, it has been necessary also to operate at relatively low formaldehyde conversions and relatively high acetylene pressures to achieve even marginally acceptable space/time yields. Where such low pressure systems have been employed, the yield and purity of product have not been sufficient to warrant commercial use of such a system. Such processes have, heretofore, involved higher operating costs than fixed bed, plug flow processes because of the higher product separation expense and have offered little in the way of savings because of the relatively poor rate of reaction and inferior catalyst life.
In general, it has been found, that unsupported active acetylide catalysts prepared from cuprous compounds, or from cupric compounds in such a way that a substantial portion of the cupric compound is reduced to cuprous copper before formation of the acetylide, tend to have a low carbon to copper ratio in which condition, they have been described as being in the form of small, sticky, relatively explosive particles, commonly containing appreciable amounts of metallic copper. Furthermore, it has been claimed in the literature that generated cuprous acetylide complex catalysts prepared from cupric compounds under an acetylene partial pressure of greater than 2 atmospheres or in the absence of formaldehyde, or in the presence of radically unbalanced amounts of acetylene or formaldehyde, or from cupric compounds which are highly soluble or dispersed in media where the compounds tend to dissolve, tend to have an insufficient total surface area and are accordingly not very effective, vis-a-vis, production of the alkynol.
A catalyst based upon high surface copper carbonate or certain other insoluble copper compounds has been described (U.S. Pat. No. 3,560,576) as one which obviates the aforedescribed difficulties. It has been shown, however, that such a catalyst is very sensitive and permanently loses activity upon being starved for either formaldehyde or acetylene and, as pointed out therein, can easily be detonated by heating to 162.degree. C.
In copending application Ser. No. 246,607, filed Apr. 24, 1972, and assigned to the assignee of this application, there is described a low pressure ethynylation catalyst comprising a water-insoluble cuprous acetylide complex catalyst supported on a magnesium silicate carrier. The catalyst disclosed therein provides substantial advantages over the cuprous acetylide complex ethynylation catalysts of the prior art such as those supported on carbon or silica including its retention of activity for long periods and its promotion of butynediol formation at an increased rate. Even though this catalyst provides substantial advantages over the other catalysts of the prior art, it has one disadvantage.
It has been found during use of the above cuprous acetylide complex -- magnesium silicate catalyst, that most of the magnesia thereof is rapidly leached from the magnesium silicate support, followed by a continuing slow dissolution of silica therefrom such that, after the reaction has reached equilibrium, about 200 ppm of dissolved silica can be found in the reaction medium. The magnesia and silica contaminate the product and may cause difficulties in further processing. In addition, this leached catalyst is relatively weak and tends to break-up into fine particles under the normal mechanical forces encountered while conducting the reaction. This causes difficulties in separating the catalyst from the product thereby resulting in increased cost of separation or in product contamination.
It would be desirable to provide an ethynylation catalyst which is active and selective for the conversion of acetylene and an aldehyde to an alkynol and which is not readily explosive, nor difficult to remove from the product nor overly active in forming cuprene. Furthermore, it would be desirable to provide such a catalyst which can be formed in situ during the reaction and which promotes substantial reaction at lower and safer acetylene reaction pressures. In addition, it would be desirable to provide such a catalyst having good physical strength and which is not soluble in the reactants or reaction products so that it can be used for long periods without contaminating the product.